Conformationally constrained analogues of glutamate have played a critical role in defining the pharmacology of the excitatory amino acid (EAA) receptors and transporters, providing valuable agonists and antagonists, and predicting binding conformations and functional group positions (e.g. COOH, NH2). While previous structure/activity studies have investigated the consequences of functional group substitutions within the EAA system, and identified a number of valuable compounds, these studies have primarily been carried out with acyclic glutamate analogues. The overall goal of this proposal is elucidate the pharmacological consequences of functional group substitution in conformationally constrained analogues. Experiments will focus on one specific group, the distal COOH moiety, and systematically substitute the distal COOH moiety with the isoelectronic NO2, SO3H, and PO3H2 groups in three conformationally constrained glutamate analogues known to interact with the EAA receptors and transporters. This library of compounds will then be assayed for: i) binding to the ionotropic glutamate receptors (NMDA, KA, AMPA), ii) activation of metabotropic receptors (ACPD), and iii) inhibition of glutamate transport systems. As the anionic groups used in these substitutions vary in size, bond orientation, charge density, and hydrogen-bonding ability, the results of this study will also provide important insight into EAA protein binding site structures and mechanisms.